1. Field of Use
This invention relates generally to apparatus and a method for reclaiming strip mined land. In particular it relates to apparatus comprising a leading tractor and a trailing tractor and an elongated angularly disposed side casting dozer blade adjustably mounted therebetween and to a method for operating such apparatus on an elongated spoil bank to shift materials therefrom into adjacent depressions.
2. Description of the Prior Art
Strip mining operations to obtain coal or other minerals are often carried out on land which originally has a generally level substantially horizontal grade. After the strip mining operation is carried out the land is left in the condition of having generally parallel spoil banks having crests spaced apart, for example, about 120 feet and extending, for example, 15 to 20 feet above the original grade, with a depression, trough or valley between each adjacent pair of spoil banks and extending, for example, 15 to 20 feet below the original grade. A side of a spoil bank and the side of the valley therebelow merge into a common slope called the "repose slope". The "repose angle" is the angle the repose slope makes with the horizontal and is determined by the particles of material settling into a state of repose under the force of gravity. Typically, the repose angle may be in the range of 26.degree. to 38.degree. from the horizontal, depending on the nature of the material forming the spoil bank and the age of the spoil bank. Heretofore it was the practice to employ conventional bulldozers or specialized forms of earth moving machinery to restore the land to its original condition by pushing or conveying the materials forming the spoil bank into the adjacent valleys. However, since a considerable volume of material needs to be moved, the use of conventional existing machinery and techniques can be very time consuming, costly and hard on equipment. It is known that land reclamation can be carried out more efficiently by, for example, a bulldozer having a blade of substantially greater width than is conventionally employed in most earth moving operations. However, the power available in a single tractor and the problem of balance limits the size of blade that can be used. It is also known to employ two or more tractors to push a single blade of relatively greater width, and U.S. Pat. No. 3,661,214 shows an arrangement wherein three tractors are disposed in side by side relationship and coupled together by a bracing structure to maintain a forced parallelism and a predetermined longitudinal relationship while they operate to push a common bulldozer blade. U.S. Pat. No. 3,552,497 teaches a generally similar arrangement. Tests have also been carried out starting in July, 1972 wherein test apparatus comprising two separate tractors of about 385 horsepower each, each having its own driver, were employed to move a common blade which was on the order of about 40 feet long and disposed at an angle of about 50.degree. with respect to the path of travel, one tractor pushing the blade and the other tractor acting to pull the blade by means of a flexible wire cable about 2 inches in diameter connected between the leading tractor and the leading end of the blade. The principal function of the leading tractor was to help counteract the side thrust forces imposed upon the blade. In the aforementioned tests the tractors exerted a combined force of about 770 horsepower on the blade. In the aforementioned test apparatus all controls for effecting changes in the position of the blade were provided between the blade and the trailing tractor and were controlled by the operator on the trailing tractor.